This invention relates to a method and device for resharpening knives for use in a machine, such as a wood cutting machine, wherein the knives are installed in a cylindrical knife mounting support.
The knives which are mounted inside the cylindrical supports of wood cutting machines are subject to rapid wear, and therefore, they frequently need to be removed and replaced by resharpened knives. Examples of this type of cutting machines are chipping machines that cut wood into chips for further industrial uses. The cutting knives which are mounted onto rims last normally only a few hours, and therefore must be exchanged several times during a work shift, which amounts to about a thousand knife changes a year.
After installing the resharpened knives in the knife rim, their cutting edges must, depending on the intended thickness of the chips, always show the same protrusion opposite the so-called wear down shoes that make up the cylindrical inner wall of the knife rim. As part of this, the knives must be mounted in such a manner that the resharpened knife edges can be adjusted outside the chipping machine by means of a special adjustment device. For this purpose each knife was until now attached in a removable manner to a support plate with a reference surface that determines the protrusion of the cutting edge and which, in turn, contacts a corresponding reference surface provided on the knife supports of the knife rim during the installation of the knife kit, consisting of knives and the knife holding plate. While it is true that this allows a reproducible protrusion of the cutting edge against the original state of the cylindrical inner wall of the knife rim, what is not being considered however, is the respective local wear condition of the inner wall. Over a longer period of time the failure to account for such local wear conditions when adjusting the position of the knives results in aconstant, and in the end no longer acceptable, increase in thickness of the chips produced.
With frequent changes of knives, the handling of the heavy knife kit is not only cumbersome, tiresome, and potentially injurious, but also time consuming; this is true especially since the knives must first be removed from their holding plates before resharpening and then remounted again. At the time of remounting, the knives' cutting edges must also be adjusted to the theoretical protrusion with regard to the before-mentioned opposite reference surface provided on the holding plate.
To avoid these disadvantages, a method and a device have been previously proposed in published German application DE 41 14 840 A.sub.1 (laid-open Nov. 22, 1992), wherein the exchange of knives in a fully and automatic manner while simultaneously adjusting the knives' edges by considering the wear condition of the wear down shoes is disclosed. With this method the cumbersome handling of the knife kit during removal and reinstallation of the knives is eliminated; however, the removed knives still have to be resharpened, individually or in groups, with special sharpening machines.
It is the underlying task of the invention to also do away with this costly step of the process without having to forego achieving a precise protrusion of the edges, matched to the respective wear condition of the wear down shoes.